The present invention is directed to voltage supplies for feeding data acquisition circuits and more particularly to fully integrated Low Voltage Floating Supply in a current sensor chip realized in monolithic high voltage technology.
FIG. 1 illustrates a circuit 10 of a single inverter leg of a common inverter application used for a motor-drive control. The circuit 10 includes a half-bridge driver 12 for driving a high side switch 14 and a low side switch 16. In such application a phase current is often sensed using a shunt resistor connected between the X node and the load. The voltage data provided by the shunt is detected by a current sensor chip 18 realized in monolithic high voltage integrated technology. Current sensing circuits, discussed in B. Murari, F. Bertotti, G. S. Vignola, “Smart power ICs” chapter 2, Sprinter-Verlag, Berlino 1996, which is incorporated herein by reference, are included in a floating n-epi pocket referred to the X node, allowing data to be detected by rejecting the common mode present at this node (VX=0V÷600V).
Typically a bootstrap capacitor CB is used to supply the floating side of the chip. The bootstrap capacitor CB is charged by a 15V source when the low side switch 16 is closed and provides VF=15V referred to VX when the high side switch 14 is closed in compliance with power transistor drive requirements. This external voltage supply VF is characterized by a ripple noise due to the charging and discharging phases on the bootstrap capacitor CB.
In general, high voltage technologies can benefit from the continuous size reduction of the MOSFETs used in signal processing circuits. In contrast, smaller devices usually require a lower than 15V supply voltage. Hence, in order to exploit the size reducing technologies, a floating supply must be realized that is capable of deriving a stable 5V supply from the VF voltage.